This invention relates to nuclear reactors and has particular relationship to the replacement of old split-pin assemblies by new split-pin assemblies in the lower guide tubes (LTG) of reactors.
Calfo discloses apparatus for carrying out this replacement. The LGT has an upper flange and a lower flange and is of substantial length, typically 124 inches to 150 inches, between the flanges. The old split-pin assembly is secured, and the new split-pin assembly is to be secured, in upper and lower counterbores in the lower flange. The LGT and the old split-pin assemblies are highly radioactive. In accordance with Calfo's teaching the replacement is effected in a work station under a pool of borated water in a plurality of successive operations, each operation carried out by a robotic tool remotely actuable from a robotic command center above the pool which is free of the hazards of radioactivity. As used in this application, the expression robotic tool means an automatic machine or mechanism which, under the commands from a command center, typically transmitted electrically, carries out predetermined operations usually on work. The operations may involve treatment of the work as well as manipulation of the work for treatment by other tools. The use of the tool may involve manual operations such as the positioning of the work for handling by the tool. The robotic tools are mounted on cluster plates on a strong back and predominantly are transportable on tracks into operating position. The cluster plates and the tools which they carry may be removed from the strong back so that maintenance and repair of separate tools may be carried out without removing the whole work station. During a split-pin replacement operation, the tools are oriented on different sides of the LGT. In addition the lower flange of the LGT carries at least two split-pin assemblies spaced 180.degree. peripherally around the lower flange. It is then necessary that the LGT be rotated to enable processing by different tools and also to enable replacement of both assemblies.
Typically the LGT is composed of stainless steel and is not only large but is also heavy. The fabricating of an LGT involves intricate machining operations whose completion consumes long time intervals. A typical LGT as completed may cost $80,000. The positioning of an LGT for processing and the rotation of the LGT during processing, without damage to the LGT, presents serious problems.
It is an object of this invention to overcome these problems and to provide a remotely-actuable robotic tool for positioning an LGT, without damage to the LGT, for processing to replace the old split-pin assemblies by new split-pin assemblies. This robotic tool, shall also have the facility of rotating the LGT as may be necessary to orient the LGT for treatment by different tools and to enable the replacement of both old split-pin assemblies with a single set of robotic tools.